Youy might want to try a different browser perhaps. It sounds like the web page isn't displaying correctly or functioning the way it is supposed to do.
You could contact Customer Service Monday to Friday http://service.mcafee.com/CustomerService.aspx?lc=1055&sg=CS&pt=1
Technical Support is http://service.mcafee.com/TechSupportHome.aspx?lc=1055&sg=TS
What is your operating system and service pack and what browser and version are you using?
Its Clealry mentioned in the above statement you have registered the McAfee Product in one of your computer, so your McAfee product was active so you have also an another option to download McAfee from McAfee site.
Please use the below link to remove the McAfee in the 2nd computer you have problems registering the McAfee
Once the McAfee product is removed click on the below link and login to your McAfee Account using the Email Address you have registered the McAfee in the 1st Computer with the Password you have created.
Click the download button and follow the on screen insructions.
Once the Installation completed you product will be active so no need for the activation and you will be all set.
For how many computers can i use the same product key?